I'm looking to tile a basement floor that was dug out about 6", so there is a roughly 6" tall x 4" wide raised concrete border around the whole room, as they didn't dig out the edges. This border is mostly level but has a rounded edge, and it's painted.

I was thinking it would be a more finished look to tile over this edge with the same thing I'm using for the floor (TBD but probably slate).

How do I do this properly so that it comes out straight?

My best guess is to use a backerboard of some kind over the existing concrete border to guarantee I have a straight, level surface on which to apply the tile. I had been planning on using Ditra for the floor, in large part just because it seemed easier (and thinner) than cement board, but would I have to worry about the interface between the two? Would I attach the cement board to the concrete just with thinset, or should it be fastened somehow? Do I need to remove the paint (it's very well adhered currently, no peeling)? Or is this completely the wrong way to do this?

1 Answer 1


If you want to ensure a perfectly straight and level corner along the entire length, then I'd suggest you build a two sided "box" to rest on the raised surface. Build it out of 1x1s, making a frame that consists of 3 long straight edges connected at perfect 90 degrees by short supports (cripples) spaced 12" on center.

Lay that box over the concrete edge, and use shims to get it perfectly level. Glue in place.

Then apply plywood to the frame and proceed with tiling as normal. (You don't need to ditra the box in this scenario, just tile to the ply)

Rough sketch showing cross section of wall/floor and stick diagram of proposed box framework: enter image description here

  • Thanks, this is a lot more simple than what I originally had in mind. I'm going to give it a shot. Do I need to worry at all about expansion/contraction of the plywood due to humidity changes?
    – Paul D
    Nov 19, 2012 at 19:26
  • If you are worried about it - if it's a humid environment - you should go ahead and use ditra as your underlayment. Nov 20, 2012 at 1:35

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